Designed to survey the meltdown, the machine completed two-thirds of its planned route

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A robot developed by the International Research Institute for Nuclear Decommissioning (IRID) and Hitachi-GE Nuclear Energy rolls on the floor in a demonstration. On Friday, it began probing inside the primary containment vessel of the No. 1 reactor at Japan's crippled Fukushima Dai-ichi nuclear plant, which suffered meltdowns following the 2011 earthquake and tsunami.

The ability to change shape hasn’t saved a robot probe from getting stuck inside a crippled Japanese nuclear reactor.

Tokyo Electric Power will likely leave the probe inside the reactor housing at the Fukushima Dai-ichi complex north of Tokyo after it stopped moving.

On Friday, the utility sent a robot for the first time into the primary containment vessel (PCV) of reactor No. 1 at the plant, which was heavily damaged by the 2011 earthquake and tsunami in northern Japan.

The pipe-crawling, snake-like robot, which can transform itself into several configurations depending on the terrain, was deployed to determine the state and location of melted-down fuel in the reactor. The move was part of efforts to extract the highly radioactive fuel and decommission the plant, a costly undertaking that will take decades.

Equipped with a thermometer, a tilting camera to capture video, a dosimeter to gauge radiation and a laser scanner to measure distance, the machine was also taking readings within the PCV.

“The robot got stuck at a point two-thirds of its way inside the PCV and we are investigating the cause,” a Tokyo Electric spokesman said via email. The machine became stuck on Friday after traveling to 14 of 18 planned checkpoints.

Tokyo Electric foresaw the possibility of the machine getting stuck, the spokesman added. The utility had planned to deploy a second robot in the PCV before the first became inoperable.

Developed by Hitachi-GE Nuclear Energy and the International Research Institute for Nuclear Decommissioning (IRID), the remote-controlled robot is 60 centimeters long and can be configured into a form resembling the letter I as well as one resembling the numeral 3.

The PCV is a huge steel container that houses another steel vessel that normally holds the uranium fuel that powers the station, as well as water.

In March, Tokyo Electric confirmed that the fuel in the No. 1 reactor had melted, complicating the extraction process. The confirmation was done via a tomography imaging scan that used elementary particles called muons.

Tens of thousands of people are still displaced due to radiation around the Fukushima plant, which is expected to cost at least ¥2.1 trillion (US$17.4 billion) to decommission.